The present invention relates to the field of signature slow down devices.
Web printing presses print a continuous web of material, such as paper. The continuous web then is cut in a cutting unit so as to form signatures that can then be folded in a folder or arranged in different manners.
Conventional quarter folders, often referred to in the art to as choppers, have an inherent speed limitation. In this regard, current technology limits the press speed to approximately 55,000 copies per hour. Moreover, to achieve even 55,000 copies per hour, two choppers typically must be placed in parallel, with consecutive signatures diverted to alternate choppers. To increase the press speed above 55,000 copies per hour, a mechanism typically must be incorporated to change the relative velocity between the press speed and the quarter folders.
Combination folders produce multiple product sizes through a series of successive folds that follow the same path through a folder. They are identified as the former old (first fold), jaw fold (second fold), digest and delta (third fold), and quarter fold (fourth fold). The product length can vary from approximately 50% to 25% of the cutoff with no lap and slightly more with lap. To accommodate this varying product length, the slow down mechanism must be flexible to have the same exit speed for all products. If not, then the folder would be forced to have a variable transmission downstream of the slow down mechanism, or the different length products would be required to travel to the delivery in alternate paths. Prior art slow down devices have generally used cylinders to slow down the signatures prior to entry into a quarter-folder or a combination folder.
U.S. Pat. No. 5,803,450 (xe2x80x9c450 patentxe2x80x9d) purports to describe a device for conveying flat floppy products (such as a signature) which includes an inlet conveyor belt with a constant velocity, an intermediate conveyor belt with a periodically changing velocity, and an outlet conveyor belt with constant velocity. The intermediate conveyor belt causes a deceleration or acceleration of the product to be conveyed. Transfer of the product between the conveyor belts takes place at respectively the same velocities of the affected belts. The drive of the intermediate conveyor belt is performed by a gear making periodic gear changes.
U.S. Pat. No. 4,506,873 (xe2x80x9c873 patentxe2x80x9d) purports to describe a high speed cross or quarter folding system for use with high speed signature transport conveyors of web printing presses. The higher speed is purportedly obtained by braking means for gradually slowing down the signature, non-linearly, as it enters the folding station, thereby allegedly preventing damage to the product or erratic folding caused by high speed impact with the fixed stop in the folder. Moving slow down stops are purportedly provided by a cyclically moving timing belt to intercept a paper product moved there into at higher speed by a conveyor. This moving stop is synchronously timed to intercept the paper product moving at a highest transit speed and is non-linearly moved to slow the paper product down to a lowest speed before it engages the fixed stop for folding. Typically a set of elliptical gears provides the non-linear timing belt slow down stop speed ratio of four to one and the system reduces the signature impact speed at the fixed stop by at least 60% from the conveyor speed of entry into the folding station.
As set forth above, prior art devices for slowing down signatures have generally utilized cylinders, which are expensive, and require sensitive make-ready and operator settings. The slow down devices purportedly described in the ""450 and ""873 patent utilize belts, rather than cylinders, to slow down the signatures. However, these devices require a greater slow down period than conventional cylinders, require make-ready, and require a phasing mechanism for the different length products associated with a combination folder. In addition, the increased slow down period results in higher forces being applied to the drive train and signature, which may cause slipping between the belts.
In accordance with the present invention, a signature slow down device is provided which includes an entrance nip mechanism for receiving a signature from an upstream device at a first signature transport velocity and reducing the transport velocity of the signature to a first reduced transport velocity; and an exit nip mechanism for receiving the signature from the entrance nip mechanism, and further reducing the transport velocity of the signature to a second reduced transport velocity. In accordance with the present invention, the respective signature contacting surfaces of the entrance and exit nip mechanisms are each defined by a pair of opposing non-circular rotating components. Each non-circular rotating component has a first surface portion for forming a nip with its opposing non-circular rotating component and a second surface portion for forming a gap with an opposing non-circular rotating component. In each of the entrance and exit nip mechanisms, the non-circular rotating components rotate at a variable velocity profile in which the non-circular rotating components decelerate when the nip is formed, and accelerate with the gap is formed.
In accordance with a first embodiment of the present invention, the entrance nip mechanism and the exit nip mechanism each include a pair of opposing cylinders, and each cylinder includes a first arc length having a first radius sufficient to form a nip between the opposing cylinders, each cylinder including a second arc length having one or more second radii, the second radii being smaller than the first radius, the second radii being sufficient to form a gap between the opposing cylinders. Preferably, the cylinders of the entrance nip mechanism are spaced apart from the cylinders of the exit nip mechanism by no more than xc2xc of the cutoff of a tabloid fold signature so that the slow down device can process delta, tabloid, and digest fold signatures. In addition, the first and second nip mechanisms preferably follow the same velocity profile. In accordance with a further aspect of this embodiment, each cylinder comprises a plurality of axially spaced apart discs.
In accordance with a second embodiment of the present invention, the entrance nip mechanism includes a entrance nip cylinder and the exit nip mechanism includes an exit nip cylinder, wherein each cylinder includes a first cylinder arc length having a first radius and a second cylinder arc length having one or more second radii, the second radii being smaller than the first radius. Most preferably, the first cylinder arc length is circular relative to the axis of rotation of the cylinder, and the second cylinder arc length is elliptical relative to the axis of rotation of the cylinder. In this regard, the arc length is defined as circular if the radius from each point along the circumference of that portion of the cylinder to the axis of rotation is constant, and the arc length is defined as elliptical if the radius from the circumference of that portion of the cylinder to the axis of rotation varies to form an elliptical shape relative to the axis of rotation.
The entrance nip mechanism further includes a first rotating belt supporting element (such as a sprocket or pulley), the exit nip mechanism further includes a second rotating belt supporting element (such as a sprocket or pulley), and a belt is mounted for rotation about the first and second belt supporting elements. The rotating belt supporting elements have a first pitch diameter arc length having the first radius and a second pitch diameter arc length having one or more second radii, the one or more second radii being smaller than the first radius. The distance between the entrance nip cylinder and the exit nip cylinder is smaller than the distance between the first and second rotating belt supporting elements such that the belt supporting elements straddle the nip cylinders. The first radius is sufficient to form a nip between the respective nip cylinder and the belt disposed over it opposing rotating supporting element and second radius is sufficient to form a gap between the respective nip cylinder and the belt disposed over it opposing rotating supporting element. Preferably, the entrance nip cylinder is spaced apart from the exit nip cylinder by no more than xc2xc of the cutoff so that the slow down device can process delta, tabloid, and digest fold signatures. In addition, the first and second nip mechanisms preferably follow the same velocity profile and have the same phase relative to the ground. Moreover, the entrance and exit nip cylinders are each preferably comprised of a plurality of axially spaced apart discs, the rotating belt supporting elements are preferably comprised of a corresponding plurality of axially spaced apart elements, and the belt is preferably comprised of a corresponding plurality of axially spaced apart belts.
In accordance with a third embodiment of the present invention, the entrance and exit nip cylinders of the second embodiment are replaced with a second pair of rotating belt supporting elements. In this embodiment, the slow down device can process delta, tabloid, and digest fold signatures without requiring a xc2xc cutoff between rotating elements.